Apples, Oranges and Roofing Underlayment: Introducing a New Testing Standard

by Paul Deffenbaugh | 1 November 2021 12:00 am

Until late-2020, the industry lacked a standard for evaluating synthetic underlayments and relied on the ASTM D226[1] and ASTM D4869[2] standards designed for felt underlayments. While synthetic underlayments have been on the market for more than 20 years, product enhancements have improved their performance over felt underlayments. Despite the differences, the industry had to rely on a testing standard designed for felt underlayments. This situation was akin to comparing apples to oranges.

Distinguishing the Benefits of Felt Versus Synthetic

The differences between synthetic and felt underlayments are many, but a key differentiator is the improved durability and performance of synthetics compared to felt. The material composition of synthetics results in a tough and durable underlayment material with improved vapor resistance and extremely high tear strength compared to felt. Asphalt felt underlayments, commonly referred to as felt paper or tar paper, have an organic core comprised of paper and sawdust that is sensitive to changes in humidity, which can result in problems including waving due to vapors or tearing around fasteners during exposure to installation foot traffic.

Synthetic underlayment can withstand extended UV exposure, vapor humidity and boot traffic as contractors install the material. Manufacturers of underlayments such as ProArmor, RhinoRoof and Titanium use the phrase “use after abuse” to describe the hardiness and performance synthetic underlayments provide even after the stress of installation.

Other benefits of synthetic underlayments relate to the marketplace. Synthetic underlayments are lighter weight, and larger rolls can mean fewer trips up and down the ladder. On any job site, safety will always be the first priority, and synthetic underlayments provide a slip-resistant surface for enhanced walkability. And, as both liquid water and moisture vapor pose a threat to metal construction, synthetic underlayments are designed and manufactured to repel water, whereas felt products tend to absorb water. Beyond its corrosive risk, accumulating moisture can also provide a breeding ground for mold and mildew.

Spearheading a New Testing Standard

Recognizing the lack of a testing standard to evaluate synthetic underlayments, Owens Corning spearheaded efforts with ASTM International’s Committee D08 on Roofing and Waterproofing and helped lead a task group that establishes appropriate, stringent performance requirements for synthetic underlayments. The group included contractors, consultants, manufacturers, testing makers and others. ASTM D8257[3] is the new testing standard established for the sole purpose of determining suitability of synthetic underlayment products for use as water-shedding underlayments in steep-slope roofing prior to and after installation of the primary roof covering.

ASTM D8257 requirements for polymeric roof underlayments set forth the physical requirements for synthetic underlayment along with specific test methods and conditions of acceptance that are appropriate for synthetic underlayment products. Some comparisons not assessed on the ASTM D226 and ASTM D4869 tests include fastener pull-through resistance, water vapor transmission, accelerated weathering, linear dimensional change, hydrostatic resistance and thermal cycling. The benefit is a much richer and substantive assessment of suitability. For example, testing a synthetic underlayment under ASTM D226 only assesses unrolling, breaking strength and pliability of the product. Such a limited assessment reveals little about a product’s suitability.

What’s Next?

With a new testing standard available, the next step becomes ensuring that it is included in upcoming building code editions—providing an opportunity for synthetic underlayments to be accurately evaluated. Owens Corning has already initiated the process of proposing that ASTM D8257 be incorporated into the 2024 I-Codes and the 2023 Florida Building Code. Inclusion in those codes for products not meeting the stringent requirements of the new standard are not code compliant. Accordingly, this standard provides a much better tool for effectively comparing apples to apples when evaluating roofing underlayments.

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Greg Keeler, is a technical services leader for Toledo, Ohio-based Owens Corning. For more information, go to www.owenscorning.com[4].

Source URL: https://www.metalconstructionnews.com/articles/apples-oranges-and-roofing-underlayment-introducing-a-new-testing-standard/

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